The present invention relates generally to a variable engine valve control system, and in particular, to engine valve control system providing variable timing and either continuously or discretely variable lift.
In general, various throttle-less systems can be used to actively control engine valves through the use of variable lift and/or variable timing so as to achieve various improvements in engine performance, fuel economy, reduced emissions, and other like aspects. Typically, such systems are mechanical VVLT (variable valve-lift and timing), electrohydraulic VVLT, or electro/mechanical VVT (variable valve-timing). In general, mechanical VVLT systems are cam-based systems, which may have additional phasers, cams and linkage. One important limitation of such mechanical VVLT systems is that the timing and lift variations are not independent. Electro/mechanical VVT systems generally replace the cam in the mechanical VVLT system with an electro-mechanical actuator. However, such systems do not provide for variable lift.
In contrast, an electrohydraulic VVLT system is controlled by electrohydraulic valves, and can generally achieve independent timing and lift controls so as to thereby provide greater control capability and power density. However, typical electrohydraulic VVLT systems are generally rather complex, can be expensive to manufacture, and typically are not as reliable or robust as mechanical systems due to their relative complexity.
Briefly stated, in one aspect of the invention, one preferred embodiment of a valve control system for an internal combustion engine includes a housing comprising a cylinder defining a longitudinal axis, and an exhaust port. A piston is disposed in the cylinder and is moveable along the longitudinal axis in a first and second direction. The piston has a first and second side. An engine valve is operably connected to the first side of the piston. An exhaust member is disposed in the housing and is variably moveable along a longitudinal path to a desired position between a maximum and minimum lift position. The exhaust member has an exhaust port that is maintained in communication with the housing exhaust port as the exhaust member is selectively, variably moved between the maximum and minimum lift positions. A pressure source applies a pressure to the second side of the piston as the piston is moved in the first direction. A control system is operably connected to exhaust member and selectively, variably moves the exhaust member to a desired position between the maximum and minimum position. The piston is moveable along the longitudinal axis in the first direction to a lift position wherein the piston blocks the exhaust member exhaust port. Preferably, the exhaust member is continuously variably moveable, meaning it is moveable between an infinite number of positions, such that the control system provides continuously variable lift control. In one preferred embodiment, the exhaust member comprises a sleeve member, while in alternative preferred embodiment, the exhaust member comprises a wedge member.
In yet another alternative preferred embodiment, the exhaust member comprises an exhaust piston. Preferably, the exhaust piston selectively communicates with a plurality of secondary exhaust ports communicating with the cylinder. In such an embodiment, the valve control system provides discrete variable lift control.
In another aspect, a preferred method for controlling an engine valve in an internal combustion engine comprises applying a force to the exhaust member with the control system, moving the exhaust member along a longitudinal path in response to the application of the force thereto, maintaining communication between the exhaust member exhaust port and the housing exhaust port, applying a pressure to the second side of the piston and thereby moving the piston and the engine valve, and blocking the exhaust member exhaust port with the piston.
The present inventions provide significant advantages over other valve control systems, and methods for controlling valve engines. For example, each of the present embodiments of the valve control system is configured as either an electrohydraulic DLVT (discrete lift, variable timing) system, which achieves discrete variable lift and variable timing for engine valves, or an electrohydraulic VVLT system, which achieves continuous variable lift and variable timing for the engine valves. In any of the preferred embodiments, relatively simple hydraulic valves can be used, which eliminates the need for position sensing and feedback controls in the system and thereby substantially reduces the complexity and cost of the system. In this way, the systems are made simpler, less expensive and more robust than conventional electrohydraulic VVLT systems. Indeed, the preferred embodiments employ relatively simple mechanisms to control the engine valve lift, and thereby de-couple the lift control operation (the slow time response part) from the timing control operation (the fast time response part). Finally, even the discrete variable lift embodiment can closely match the performance of conventional VVLT systems, under most operating conditions, by providing a plurality of discrete variable lift positions within the system.